Effect of combinative addition of strontium and rare earth elements on corrosion resistance of AZ91D magnesium alloy

The influencf of strontium（Sr） and rare earth（RE） elements on the corrosion behavior of AZ91D magnesium alloy was investigated by conventional corrosion testing and electrochemical measurements in 3.5% NaCl solution. After comparing the mass loss and hydrogen evolution of the samples, the microstructures of the alloys and the morphologies of their corrosion product films were characterized by electron probe microanalysis-energy dispersive spectrometry（EPMA-EDS） and Auger electron spectroscopy（AES）. Compared with individual addition of Sr or RE to AZ91D, the combinative addition of 0.5% Sr and 1% RE to AZ91D successfully decreases the corrosion rate further, which can be attributed to the depression of micro-galvanic couples, as well as the formation of more protective film due to aluminum enrichment. The combinative addition of strontium and rare earth elements to AZ91D magnesium alloy appears to be a promising approach to increase its corrosion resistance.     

AZ91D镁合金在含SO_2大气环境中的初期腐蚀行为

采用室内加速的方法,利用金相显微镜、扫描电镜和X射线衍射等手段对AZ91D镁合金在含微量SO2工业污染环境中的初期腐蚀层形貌以及腐蚀产物进行了分析和研究。结果表明:SO2加速镁合金的腐蚀,随着SO2含量增加,镁的腐蚀速率加快。镁合金的初期腐蚀具有局部腐蚀的特征。腐蚀优先从α相基体开始,腐蚀初期在材料表面生成一层保护性的含有MgO和Mg(OH)2的薄膜。SO2降低了薄液层的pH值,增强溶解过程,促进可溶性MgSO3·6H2O和MgSO4·6H2O腐蚀产物的生成,使表面膜失去保护作用,加速镁合金的后期腐蚀。     

Influence of chemical composition on corrosion resistanceof AZ91D magnesium alloy ingots

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AZ91镁合金脉冲电沉积Ni-SiC纳米复合涂层的磨损与腐蚀性能

为了改善AZ91镁合金的表面性能,在含0-15g／LSiC纳米颗粒的改进的瓦特槽中,采用脉冲电沉积得到不同SiC含量的Ni-SiC纳米复合涂层。采用扫描电子显微镜（SEM）研究涂层的形貌,采用能谱仪（EDs）测试涂层的SiC含量。从15g／LSiC槽中电沉积得到的样品,其涂层的显微硬度提高了600％。采用动电位极化法研究包覆AZ91镁合金的腐蚀行为。结果表明,样品的耐腐蚀性能明显提高,即腐蚀电流密度从未包覆样品的0．13mA／cm2降低到槽中含15∥LSiC电沉积包覆样品的1．74x101mA／cm2,腐蚀电位从未包覆样品的-1．6V增加到槽中电沉积包覆样品的-0．31V。使用盘销摩擦测试仪评估了包覆和未包覆样品的耐磨性能,包覆样品的磨损量比未包覆的小8倍。     

Influence of rare earth element Ce and La addition on corrosion behavior of AZ91 magnesium alloy

Two types of AZ91 magnesium alloys containing rare earth element Ce or La were fabricated. Hydrogen evolution and electrochemical tests were carried out to evaluate the corrosion behavior of new AZRE (RE = Ce or La) and AZ91 alloys in 3.5% NaCl solutions (pH 6.50). Various corrosion rate tests indicated that addition of RE obviously enhanced corrosion resistance of AZ91 magnesium alloy. The optimal content of RE was 0.92% for Ce and 0.66% for La. Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and low‐angle X‐ray diffraction (XRD) were used to characterize the effect of RE addition on microstructure and corrosion product film of AZ91 magnesium alloy. The refined β phase and formation of γ phase in AZRE alloy were observed by SEM, which resulted in the improvement of corrosion resistance due to the depression of microgalvanic couples. Moreover, the enhanced protective effectiveness of corrosion products was another reason for the improved corrosion resistance.     

Organic-magnesium complex conversion coating on AZ91D magnesium alloy

An organic-magnesium complex conversion (OMCC) coating on AZ91D magnesium alloy was obtained by treating in a solution containing organic compounds. SEM, FESEM and XPS were used to examine the surface morphology, thickness and structure of the conversion coatings. The results show that the continuous and uniform conversion coating is deposited on AZ91D alloy and the main component of the coatings is organic compound containing benzene ring, which forms a chemical bond with magnesium. The polarization measurement and salt spray test show that the corrosion resistance of the conversion coating is much higher than that of traditional chromate conversion coating.     

添加稀土Er于熔剂中对铸态AZ91镁合金组织与性能的影响

研究了熔炼时在熔剂(42%MnCl2 53%LiCl 5?F2,质量分数,%)中添加稀土Er对铸态AZ91镁合金显微组织、力学性能、断口形貌以及腐蚀行为的影响。结果表明:在熔剂中添加稀土Er能够去除镁合金熔炼过程中产生的熔剂夹杂,净化镁合金熔体,提高铸态AZ91镁合金的拉伸性能和耐腐蚀性能;当熔剂中添加10%的稀土Er时,镁合金的抗拉强度σb和伸长率δ分别从156MPa和1.8%上升到最大值220MPa和4.1%;同时,镁合金在5%NaCl水溶液中的腐蚀速率从1.20mg/(cm2.d)下降到最小值0.15mg/(cm2.d);然而,随着稀土Er在熔剂中添加量的进一步提高,合金中开始有φ-(Al7ErMn5)和τ-(Al66.7Mg23.3Er10)等含有稀土Er的相生成,消耗了合金中的Al和Mn元素,改变了β-(Mg17Al12)相的形态;而且沿枝晶界附近分布的粗大φ-(Al7ErMn5)相降低了枝晶之间的结合力,使得合金的σb和δ下降;同时,部分网状的β-(Mg17Al12)相断裂,呈离散的块状,导致合金的腐蚀速率增加;熔剂中添加稀土Er不改变镁合金的断裂机理,断裂机制仍为准解理断裂。     

AZ91D镁合金的均一化前处理与化学镀Ni-P

采用新型环保的均一化前处理工艺在AZ91D镁合金表面制备了化学镀Ni-P镀层。研究了前处理过程中AZ91D基体微观形貌、镀层沉积过程、成分和相结构。研究结果表明：基体表面的β相在前处理过程中被选择性去除,表面组织得到均一化,从而获得均匀致密的浸Zn层。Ni-P颗粒均匀形核生长,并最终形成致密的镀层。镀层具有优良的耐腐蚀性能。     

Electrochemical noise characteristics in corrosion process of AZ91D magnesium alloy in neutral chloride solution

The corrosion process of AZ91D magnesium alloy in neutral 1% (mass fraction) sodium chloride aqueous solution was investigated by electrochemical noise(EN), SEM and EDX. Fractal theory was primarily used to depict the corrosion process of the alloy. The fast wavelet transform(FWT), as well as the fast Fourier transform(FFT), was employed to analyze the EN data. The results show that the overall corrosion process can be described by three stages. The first stage corresponds to the pit nucleation and growth; the second stage involves the growth of a passive oxide layer; and the third stage involves reactivation. With increasing immersion time, fractal dimension increases fast initially, fluctuates in the medium and increases again at last. Pitting corrosion and fractal dimension increase due to the initiation and formation of pits in the initial and the end of immersion, while depresses due to the passivation in the medium period. The results of SEM and EDX support the above conclusions.     

AZ91D薄板搅拌摩擦焊

实现了厚度为2.2 mm铸造镁合金AZ91D薄板的搅拌摩擦焊和钨极氩弧焊,分析了搅拌摩擦焊工艺参数对焊接接头成形的影响和接头组织变化,考察了搅拌摩擦焊接头的力学性能.在搅拌头旋转速度为1 380 r/min时得到了比较理想的焊接接头,而1 960 r/min的转速过大.接头不同区域所受的机械力和热量不同,显微组织明显不同.搅拌区晶粒细小,显微硬度和强度都有所提高.搅拌摩擦焊接头力学性能与热输入有关;与氩弧焊接头相比,搅拌摩擦焊接接头的性能更好.     

Barium phosphate conversion coating on die-cast AZ91D magnesium alloy

Poor corrosion resistance limits the application of magnesium alloys.Conversion coating is widely used to protect magnesium alloys because of easy operation and low cost.A novel conversion coating on die-cast AZ91D magnesium alloy containing barium salts was studied.The optimum concentrations of Ba(NO_3)_2,Mn(NO_3)_2 and NH_4H_2PO_4 are 25 g/L,15 mL/L and 20 g/L,respectively,based on orthogonal test results.The treating time,solution temperature and pH value are settled to be 5-30 min, 50-70℃and 2.35-3.0...     

AZ91D镁合金手汗腐蚀机理研究Ⅲ乳酸对AZ91D镁合金的腐蚀机制

通过电化学阻抗(EIS)和动电位极化曲线等方法研究了镁合金在乳酸和含有Cl^-的溶液中的电化学特性，发现镁合金腐蚀过程受到电极电位E、以β相为中心向外扩展的表面氧化膜的覆盖面积θ和MgH2的浓度Cm 3个表面状态变量的控制，在腐蚀过程中，β相表面氧化膜向四周扩展，覆盖了邻近很小范围的α相晶粒，从而使部分α相晶粒不受腐蚀．最后通过理论推导建立了一个新的镁合金腐蚀理论模型，并利用EIS实验证实了模型的可靠性。     

Thixotropic behavior of semi-solid AZ91D magnesium alloy

The thixotropie behavior of semi-solid AZ91D slurry was studied through a Couette type viseometer.The results show that the apparent viscosity of semi-solid AZ91D magnesium alloy slurry increases after being isothermally held, but the apparent viscosity quickly falls down to a steady state value after being stirred again and it takes on a sharp shear-thinning behavior. With the same shearing rate and the rest time increasing, the steady apparent viscosity increases because of the agglomeration of the solid particles, and the time required for the slurry to reach the steady state also becomes longer. If the solid fraction increases, it takes longer time for the slurry to reach the steady apparent viscosity with the same shearing rate and the same rest time. If the solid fraction and the rest time are the same, but the shearing rate rises, it takes shorter time for the slurry to reach the steady apparent viscosity and the final steady apparent viscosity also decreases.     

Anodization of AZ91 magnesium alloy in alkaline solution containing silicate and corrosion properties of anodized films

The anodization of AZ91 magnesium alloy in an alkaline electrolyte of 100g/L NaOH 20g/L Na2B4O7·10H2O 50g/L C6H5Na3O7·2H2O 60g/L Na2SiO3·9H2O was studied.The corrosion resistance of the anodized films was studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques.The microstructure of the films was examined with scanning electronic microscope (SEM) and X-ray diffractometer (XRD).The results show that,under the experimental conditions,the optimum anodizing time and the optimum anodizing current density are 40min and 20mA/cm2 respectively for obtaining the anodic film with high corrosion resistance.The XRD pattern shows that the components of the anodized film consist of MgO and Mg2 (SiO4).     

AZ91D镁合金半固态触变成形的数值模拟

采用商业有限元软件DEFORM3DTM对半固态镁合金AZ91D的触变成形过程进行了数值模拟,并利用自制的模具,在加热到570℃保温不同时间的情况下,对AZ91D镁合金半固态坯料进行触变成形试验。通过模拟分析的结果与试验的实际结果进行对比,得出了最佳触变成形工艺参数,同时,在一定程度上验证了数值模拟分析结果的可靠性。     

电解液组分对镁合金微弧氧化成膜及膜层耐蚀性的影响

基于单纯形重心设计改变Na₂SiO₃、NaOH、KF和NaAlO₂ 4种组分的搭配,在AZ91D镁合金上进行微弧氧化处理,研究了电解液配方对膜层成膜及耐蚀性能的影响。结果表明,所得到的回归方程非常显著,预测精度高。帕累托分析显示,4种电解质均对膜层耐蚀性影响显著。通过响应面分析可知,增大主盐Na₂SiO₃或者NaAlO₂的浓度可以显著提高膜层的耐蚀性。但二者复合却不利于耐蚀性的提高。主盐对于提高膜层成膜性及耐蚀性至关重要。当电解液中无主盐时,膜层的成膜性及耐蚀性都很差。当电解液中含有主盐时,适当增加NaOH与KF的浓度,膜层耐蚀性提高。通过Pearson相关分析可知,膜层耐蚀性主要受致密度及孔隙率的影响,同时也受膜厚、物相等其他特征参量的影响。而电解液各组分通过影响上述微观结构特征参量从而影响膜层性能。     

固相合成AZ91D镁合金的组织和性能

利用固相合成方法在挤压比为11∶1的条件下,将AZ91D镁合金屑分别在573、623、673和723 K时制备成试样,对试样进行微观组织观察和力学性能测试。结果表明:在573~673 K时,AZ91D镁合金的抗拉强度和延伸率随合成温度的升高而增大,高于673 K时其抗拉强度和延伸率随合成温度的升高而降低,在合成温度为673 K时,其抗拉强度最高,达到384.4 MPa;在热挤出过程中氧化层被均匀弥散在组织中且发生动态再结晶,使固相合成AZ91D镁合金的力学性能与铸态和用铸锭热挤出制备的镁合金相比明显提高,在合成温度为673 K时,其延伸率为5.8%,比铸态增加152%;AZ91D镁合金屑在挤出过程中不能完全结合且出现较多的微裂纹,使其延伸率与铸锭热挤出制备的AZ91D镁合金相比低44%。     

A novel dual nickel coating on AZ91D magnesium alloy

Magnesium alloys covered with metal coating display excellent corrosion resistance,wear resistance,conductivity and electromagnetic shielding properties.The electroless plating Ni-P as bottom layer following the electroplating nickel as surface layer on AZ91D magnesium alloy was investigated.The coating surface morphology was observed with SEM and the structure was analyzed with XRD.Electrochemical tests and salt spray tests were carried out to study the corrosion resistance.The experimental results indi...